'The ways were foul and narrow; the shops and houses wretched; the people half-naked, drunken, slipshod, ugly. Alleys and archways, like so many cesspools, disgorged their offences of smell, and dirt, and life, upon the straggling streets; and the whole quarter reeked with crime, with filth, and misery." This could easily have been a criticism of the St Paul's Occupy camp made in any number of newspapers. "I am so pleased and so happy they have finally gone. It has been grubby and the site has smelled," a City worker called Joanna told the Daily Telegraph. In fact the passage is from Dickens – A Christmas Carol – and one George Orwell points to as evidence that Dickens, for all his burning social conscience, was revolted by poverty and sought to keep at a respectable distance from it. In Dickens, revulsion slides into moral blame.

Others have made this connection more overtly. The conservative bioethicist Leon Kass, in constructing a case against genetic cloning, speaks of "the wisdom of repugnance". Similarly Lord Devlin, back in 1959 when arguing against the liberalisation of laws concerning homosexuality, insisted that "intolerance, indignation and disgust … are the forces behind the moral law". Tea Party Republican Carl Paladino even impregnated his political flyers condemning a rival candidate with the stench of rotten cabbage.

"You stink" is more than just a playground taunt. For a moralised version of disgust has regularly been used as the rhetorical weapon of choice against a whole range of people – against "foreigners" and women and homosexuals in particular. And what often gets emphasised in this visceral form of moral assault is the presence of human bodily products: piss, shit, sweat, dead skin, snot, pus, saliva, semen, and blood, especially menstrual blood.

But doesn't this moralised version of disgust represent some deep-seated hostility to the constituent elements of our humanity? Human beings smell. And being revolted by human smell feels troublingly connected with being revolted by human beings themselves. For indeed, to love another human being is intimately bound up with what they smell like. And that has nothing much to do with Chanel No 5. Making love is an act of passionate immersion in the physical reality of the other. Which is precisely why Mellors was so engaging as Lady Chatterley's lover: "I don't want a woman as couldna shit nor piss."

So how is disgust supposed to relate to moral harm? Because it is perceived to be an indicator of what is bad. Most who study disgust give it an evolutionary function. Disgust represents a fear of contamination. And a great many traditional social boundaries and taboos exist as a way of protecting against contamination. The anthropologist Mary Douglas famously argued that the desire for purity and cleanliness is all about organising offensive things into acceptable social spaces – a place for everything and everything in its place. But the problem with a moral instinct that's all about policing the social boundaries created by disgust is that the sources of disgust are often the very same things that make us human. Cardinal O'Brien, for instance, is filled with disgust at the thought of gay sex. Which is why he is so intent on maintaining the boundaries of traditional marriage. But what a great many of us see in the Catholic church's response to homosexuality is simply a refusal of love itself – more specifically, love in all its sticky, squelchy reality.

The dirty protests in Northern Ireland by Republican prisoners, who smeared the walls of their cells with their own excrement, were the most extreme politicisation of shit. These protests have recently returned in Maghaberry prison, in response to forced strip searches. If strip searches dehumanise, shit aggressively reasserts the prisoner's humanity. I shit therefore I am.

But what asserts humanity also revolts. And revulsion is precisely the reaction that a few months in a tent are bound to amplify, as the screwed up grimaces of bankers passing through St Paul's churchyard have indicated. It wasn't the protest against capitalism per se that offended the conservative mindset; the problem was that the so-called soap dodgers were out of place. They represented a reaction against what the philosopher Thomas Nagel has recently called "a carefully controlled and cleaned up version of ourselves". "Reminders of the mess that lies beneath," he continues, "can cause us to shrink away in disgust."

Having money and power are some of the most effective ways of keeping raw humanity at bay. They work as a prophylactic against the visceral aspects of human life. Basically, you get other people to deal with the shit. Occupy reminded the City that this vanilla version of humanity is a false consciousness. It is a disturbing message that we often desperately avoid. Little wonder the first thing the City of London did after the protesters had been cleared away was to bring in the sanitation unit.